Retinal neurons express unusual responses to neurotransmitters, including antagonist-insensitive GABA responses, and glutamate-evoked hyperpolarizations. The project goals are 1) to study responses of retinal neurons to exogenous pharmacological stimuli, as well as natural light stimuli, and 2) to understand the relationships between receptor expression on retinal neurons, the neural circuitry of retina, and retinal information-processing tasks. The study examines acutely dissociated retinal neurons from rat and zebrafish, and in situ neurons identified in zebrafish retinal slices. Acutely dissociated bipolar and horizontal cells retain their shapes and can be morphologically identified in culture. Cells in retinal slices are identified morphologically by intracellular dye injection via the recording electrode. Physiological responses of isolated cells are assayed with voltage-sensitive probes; whole-cell patch clamp techniques are used to record the responses of neurons in the retinal slice. Dissemination of knowledge in retinal neurobiology through WEBVISION (http : //insight. med. utah. edu/Webvision/index. html), an internet-based tutorial, continues to be a subsidiary goal of this project. Chapters on horizontal cell physiology and retinal glutamate receptors have recently been added. A survey of pharmacological properties of acutely dissociated rat retinal bipolar cells (BCs), and other dissociated rat retinal cells (RCs) has been completed. Neural responses were assayed with the non-invasive, fluorescent (FL), voltage-sensitive probe oxonol DiBaC4(5). Inhibitory agonists GABA, TACA, glycine, and R(+)baclofen evoked hyperpolarizations (FL decreases) in 70-100% of responsive cells. Bicuculline-resistant GABA responses occurred in approximately 80% of GABA-responsive RC's and BC's alike. Both bicuculline-sensitive (GABA-A like) and bicuculline- insensitive (GABA-C like) responses were resistant to picrotoxin. L- glutamate and kainic-acid evoked responses of either polarity in BC's and RCs. Hyperpolarizations predominated in BC's while depolarizations (FL increases) predominated in RCs, both response types were blocked by CNQX. Substitution of sodium by N-methyl-D-glucamine (NMG) after gramicidin treatment (1 muM) produced a series of cellular FL changes suggestive of a technique sensitivity approximately 70 mV per decade change in FL. The oxonol probe technique is currently being applied to glutamate responses of dissociated bipolar and horizontal cells of zebrafish retina, in conjunction with parallel studies of glutamate-evoked currents measured using whole-cell patch clamp techniques.